Switzerland comprises less than 4% of the global stock market, so for most American investors who aren’t currency speculators the surge didn’t directly have a large impact on their portfolios. But it was later revealed that a hedge fund, Everest Capital’s Global Fund, was essentially wiped out by the currency swing. And there were likely a number of other funds that were buffeted as well.

The travails of such funds highlight the importance of knowing what you own in your portfolio. “Knowing what you own” doesn’t mean memorizing the names of all your holdings or learning facts about each one. Instead it means having a high-level understanding of how the different pieces of your portfolio fit together: which asset classes, sectors, and regions of the world your portfolio is exposed to.

Having a clear understanding of these exposures can help ensure that your portfolio won’t be decimated when the price of some asset swings wildly, as occasionally happens. A sudden 20% movement for a currency as prominent in the global economy as the Swiss Franc is extremely rare. But with so many possible occurrences in financial markets, outcomes that individually seem like they should be rare actually happen fairly frequently. The price of a major commodity such as oil falling by 50% in a 6-month period is also a rare occurrence, for example, but such a plunge happened in the second half of 2014 (and an even larger one occurred only 6 years earlier, in 2008).

Trying to predict each one of these rare events would be a fool’s errand. Knowing what you own, and therefore being able to avoid any concentrated exposures that could ravage your portfolio, is a simpler and more rewarding alternative.